Since Robert M. Gage invented the process of plasma arc welding (PAW) and plasma arc cutting (PAC) in 1953, it has evolved in the technological age to become a very productive way to weld and cut sheet metal, both by hand and by robots.
Computer numerical control plasma cutters are programmed by software to create patterns. In the 1980's this was restricted to flat tables, but today, new vertical CNC plasma cutting machines are available, providing products for everyday consumers like artistic metalwork for gardens and walls, as well as for traditional industrial use.
Plasma welding, like TIG welding and gas tungsten welding, forms an arc between a tungsten electrode and the work piece, however, the plasma arc can be separated from the shielding gas envelope by positioning the electrode within the body of the torch. The advantage plasma welding and cutting offer over other processes is that there is hardly any distortion because there is very little heat exposed to the job.
Usually, a direct current (DC) power source with dropping characteristics and a 70 volt plus open circuit is suitable for plasma arc welding, while purpose built plasma systems are available. It is also possible to add a plasma control console to a conventional TIG power source.
The combination of gases used is usually Argon for the plasma gas and Hydrogen for the shielding gas. Helium can be used, but its heat reduces the current rating of the plasma nozzle, making it unsuitable for the keyhole plasma application.
There are three main applications for plasma welding and cutting. These are:
- Microplasma - 01 to 15A, traditionally used for welding thin sheets and wire and mesh and minimises arc distortion.
- Medium current - 15 to 200A, an alternative to TIG with the advantage of tolerance to surface contamination.
- Keyhole plasma - Over 100A for thicker stainless steel. When used with filler it ensures a smooth weld profile.
Once quite expensive, modern plasma torches are now affordable even for hobbyists. Lighter units and near-laser precision has created a growing number of customers, adding to the growth and development of the welding industry.